Obviously, if you have luggage to check, you'll still have to visit the counter.

The mobile website is currently in beta.

As for mobile boarding passes: United passengers departing from one of eight U.S. airports will receive an e-mail with an encrypted two-dimensional QR barcode that stores their flight, seat assignment and gate information.

The barcode, visible on the phone's display, is scanned by Transportation Security Administration agents at the appropriate checkpoints.

(The TSA still requires flyers to show photo identification, however. Baby steps.)

The eight airports:

Chicago O'Hare

Dallas-Fort Worth

Denver

Las Vegas

Los Angeles

New York La Guardia

San Francisco

Washington Dulles

Orlando, Philadelphia, Phoenix, Portland and Seattle are slated to be included next.

The TSA has been urging carriers to roll out the program for several reasons: it's green, it's convenient, it's harder to lose and it's more secure, because it can't be printed at home.

Unlike the usual one dimensional single line bar code you would normally see on a box of Cap'n Crunch, this bar code is two dimensional. The encrypted code contains passenger information as well as authentication information from the airline that can only be decoded by a TSA scanner. TSA is also working with the airlines to create the same type of bar code for those who choose to use paper boarding passes. How is it tamper resistant you might ask? Well, I guess you could manipulate the code if you really wanted to, but the scanner will detect any sign of tampering.

United's program applies to passengers traveling within the United States, Puerto Rico or the U.S. Virgin Islands.

United's not the only airline trying out paperless boarding passes: American Airlinesrecently announced that it is expanding its two-year-old program to 27 airports, from eight, including Washington Dulles International, New York La Guardia and San Francisco International.